RGB LED driver, Any comments?

[peu]

Hey Peu, I'm working on pretty much the same thing with a 12F675 PWMing to 3 Mosfets. Everything is working well except I'm finding when I PWM from GP2 and GP4 the MOSFETs don't really pulse they pretty much just stay on, or switch off when the cycle gets low enough. I'm not sure why, I've poked the ANSEL and CMCON, but it seems maybe the output voltage on those pins is a little different or something. Anyone have any ideas what might be going on? I see you are driving your green channel with GP2, does that work fine for you?

I used this header in a previous version that used gpio.0 as an adc input and 1,2 and 4 as the pwm channels

@ device pic12F683, intrc_osc_noclkout, wdt_on, mclr_off, protect_off
@ device INTRC_OSC_NOCLKOUT
DEFINE OSC 4

trisio =%00000001
ansel =%00000001 'analog off except gpio.0
cmcon0 =%00000111 'Comparators Off
pasos con 16
ciclos con 10
conta var byte
puerto var byte


and this is the routine I use for the led brightness increase:

for conta=0 to 255 step pasos 'Rise routine
pwm puerto, conta, ciclos ; puerto is the port to be used
next conta
high puerto ; after it reached the top brightness, set port high
return


you can use the same routine for decreasing, just change the for next and put a LOW after the loop instead of the high.

hope it helps


Pablo

[KD6OJI]

Try using a 1K pull down from the gate to ground on your MOSFET's. I have found that sometimes they get a little flaky with PWM and the 1K seems to make a huge difference.

[ERIK]

Ya did put some 1K's on and found the same thing, that it all worked perfectly. I should've come back to this post with that. Strange that I haven't seen any mention of doing that anywhere else.

[paxmowa]

I don't know for sure,

since i changed my computer I should digg out the old schematics somewhere. But I'm pretty sure that there where pulldown resistors in my design. It's never a good thing to leave the pics pin floating in mid air, which will always cause weird results.

This being said, does anyone think it's feasable to design a RGB christmas light with 50 channels from one PIC controller, prefferably 16C class? I don't think it can be done. Last year with the 8 channel set-up, it was already clear that the switching between the colours was getting a bit iffy to say the least, colours bleeded a bit from one transistion to another when working with 2 or more colours at the same time. I would use decimal counters to go down the row of leds, but I don't think it could be switched fast enough to at least have a flicker-free view.

It was programmed like this:

set pwm for red - green - blue
turn on all used channels
wait a few msec
turn off all channels
set pwm for red - green - blue
turn on all used channels
wait a few msec
turn off all channels
etc...

When I wanted one out of two leds to be red and the other ones blue, I ended up with a light shade of blue and a shade of pink, which made me think the PWM channels didn't ramp down fast enough or something.

Steve